1. Field of Invention
The present invention relates generally to the field of oilfield exploration, production, and testing, and more specifically to compositions, apparatus comprising these compositions, and methods of using same.
2. Related Art
Existing structural compositions, that is materials and combinations of materials, have been developed to sustain elevated loads (forces, stresses, and pressures) at useful ranges of temperatures, and also not to react, and thus degrade by dissolving, disintegrating, or both in the presence of common fluids such as water, or moist air. Note, for a better understanding of the invention, that a composition is here defined as a tangible element created by arranging several components, or sub-compositions, to form a unified whole; the definition of composition is therefore expanded well beyond material chemical composition and includes all combinations of materials that are used smartly to achieve the purposes of the invention.
Structural compositions found in everyday applications (mainly metals and alloys) are required to be durable over intended element lifetimes; i.e. they must be chemically inert, or not reactive, even though many rust or corrode over the intended element lifetimes. In generic terms, a reactive metal may be defined as one that readily combines with oxygen to form very stable oxides, one that also interacts with water and produces diatomic hydrogen, and/or one that becomes easily embrittled by interstitial absorption of oxygen, hydrogen, nitrogen, or other non-metallic elements. There are clearly various levels of reactivity between metals, alloys, or in general compositions, or simply any element listed on the periodic table. For instance, compared to iron or steels (i.e. alloys of iron), aluminum, magnesium, calcium and lithium are reactive; lithium being the most reactive, or least inert of all four. Reactive metals are properly grouped in the first two columns of the Periodic Table of the Elements (sometimes referred to as Column I and II elements); i.e., among the alkaline and alkaline-earth elements. Of the alkaline metals, namely lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), and alkaline-earth metals, namely beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), radium (Ra), few may be directly utilized for the excellent reasons that they are either 1) far too reactive to be handled safely and thus be readily procurable to be useful for any commercial applications, or 2) not sufficiently reactive as they for instance passivate in aqueous environments and thus form stable protective barriers (e.g. adherent oxides and hydroxide films), or 3) their rate of reaction or transformation, and thus degradation, is too slow, as it is for instance seen when magnesium, aluminum and their commercial alloys are immersed in cold and neutral water (i.e. neither acidic nor basic; pH=7). Though profoundly less reactive than the alkaline and alkaline-earth metals, aluminum may be also included among the reactive metals. Yet, aluminum does not react, or degrade with water nearly to the same extents as the Columns I and II elements since aluminum is a typical material used in durable elements for applications as diverse as automotive, aerospace, appliances, electrical, decoration, and the like. To quantify reactivity of an element, galvanic corrosion potentials may be used, or if unavailable measured, as for instance for any novel composition compared to a reference, for instance the hydrogen reaction; for instance the higher the potential of a composition with respect to hydrogen the lesser its reactivity and its likelihood to degrade noticeably, or rapidly. Because reactivity of an element is linked to the ease chemical reactions proceed with non-metallic elements (e.g. oxygen, nitrogen), for periodic table elements electronegativity constitutes an excellent measure of reactivity. Electronegativity, and especially corrosion potential of aluminum are sufficiently low compared to the other elements of the periodic table to categorize aluminum as a reactive metal rather than a non-reactive, inert or noble metal or element.
In numerous environments, including in the oilfield but not exclusively, it would be advantageous to be able to utilize a component comprised of a reactive composition comprising alkaline, alkaline-earth elements, or other metal (e.g. aluminum) having either an enhanced reactivity (e.g. compositions comprising aluminum) or reduced reactivity (e.g. compositions comprising calcium) relative to that of the (pure or unalloyed) alkaline or alkaline-earth elements in the composition. It would also be of great benefit to controllably enhance or delay the interaction or degradation of the reactive compositions with its fluidic environment; an environment that may comprise water, completion fluids, and the like and will therefore be corrosive to the inventive composition. The compositions of interest are those that degrade by either dissolving or disintegrating, or both when demanded by the application or the user. The degradation may proceed within minutes, hours, days or weeks depending upon the application requirements; in oilfield environments typical time for degradation may range from minutes to days, occasionally weeks.
Among the multitude of oilfield examples that may be foreseen for degradable compositions is that of a diverter ball. A diverter ball is a solid object that is dropped or pumped through wellbore tubulars in a process known as diversion and may be utilized in operations known as acidizing and fracturing. Both acidizing and fracturing are well-known operations to the skilled artisan and require little further explanation. In other well operations, perhaps less well-known than the latter, balls are employed as downhole valves in different fracturing zones by serving as temporary plugs to isolate fluids from different zones. In the present context the term “ball” extends beyond that typically associated to spherical shapes and includes bars, plugs, darts, and any other shaped members, and is more generally referred to herein as well operating elements.
In previously-known well operations, diverter balls and fracturing elements are either flowed to the surface or dropped to the bottom of the wellbore once their function is completed. Since they are not degradable in the wellbore environment, or their rate or location of dissolution are essentially uncontrolled or extremely sluggish their use has been nearly non-existent. In some applications, the dissolvable composition loses structural integrity and thus its ability to isolate fluids from distinct zones from mechanical action, contact with a fluid, heat, or combination thereof, and before dissolving it may be pumped to the surface with well fluids, or dropped to the bottom of the wellbore.
In many well operations, including diverter balls, it is desirable to possess well operating elements that controllably degrade either in rate, location of the element, or both (or include a portion that predictably degrades) in the wellbore environment, without having to resort to highly acid conditions, high temperatures, mechanical milling, or a combination of these. Since none of the known drop balls, diverter balls, and the like have the ability to degrade in a controlled user defined fashion, such degradable elements, and compositions could potentially be in high demand in both the oilfield and elsewhere, as further detailed in subsequent sections.